The present invention relates to an electronic alarm circuit for operating an audible alarm such as an electro-mechanical buzzer or a bell. This electronic alarm circuit provides discrimination between the sound of the alarm on test and the sound indicating a real alarm.
Known alarm circuits include a buzzer which is triggered by means of the closure of a remote, normally open switch. Such a circuit has the following disadvantages:
in order to check that the buzzer and the line connecting the switch to the buzzer are working it is necessary to short-circuit the terminals of the switch. However, the switch is often remote from the test centre where the buzzer is located and may even be inaccessible;
the test produces an audible signal which can be interpreted as a real alarm;
bad contacts producing transient faults may exist in the circuit, but may not be detected by the test.
The alarm circuit of the invention seeks to minimize these disadvantages.